Java Cookbook

Simplifying Your JSP with a JavaBean

Problem

You want to reduce the amount of Java coding in your JSP using a JavaBean component.

Solution

Use <jsp:useBean> with the name of your bean.

Discussion

JavaBeans is Java’s component technology, analogous to COM components on MS-Windows. Recipes Section 23.8 and Section 23.9 contain a formula for packaging certain Java classes as JavaBeans. While JavaBeans were originally introduced as client-side, GUI-builder-friendly components, there is nothing in the JavaBeans specification that limits their use to the client-side or GUI. In fact, it’s fairly common to use JavaBean components with a JSP. It’s also easy and useful, so let’s see how to do it.

At the bare minimum, a JavaBean is an object that has a public no-argument constructor and follows the set/get paradigm. This means that there is regularity in the get and set methods. Consider a class, each instance of which represents one user account on a login-based web site. For the name, for example, the methods:

public void setName(String name);
public String getName(  );

allow other classes full control over the “name” field in the class but with some degree of encapsulation; that is, the program doesn’t have to know the actual name of the field (which might be name, or myName, or anything else suitable). Other programs can even get a list of your get/set methods using introspection (see Section 25.3). Example 18-14 is the full class file; as you can see, it is mostly concerned with these set and ...